Growth stresses and their consequences on tree mechanics - Archive ouverte HAL
Communication Dans Un Congrès Année : 2018

Growth stresses and their consequences on tree mechanics

Delphine Jullien

Résumé

During tree growth, mechanical stresses accumulate in the trunk and branches due to the increasing weight and wood maturation. The progressive increase of the weight of the tree induces self-support stress whose distribution is very different from a homogeneous beam with load uniformly distributed over its section. Because the vertical position is challenging gravity, increase in tree weight during growth may disturb the mechanical equilibrium of the stems or branches. During the formation of a new wood layer at the periphery of the stem or branch, physico-chemical transformations occurring with the thickening of the cell wall generate mechanical stresses at periphery, called maturation stress, and used by the tree to control posture and preserve shape in a standing position. The combination of self-support stress and maturation stress is called growth stresses. Measuring the corresponding released strain at the periphery of stems may evidence maturation stress: isolating a piece of stressed wood from surrounding tissues leads to shrinkage if the stress is tensile, swelling if the stress is compressive. These measurements may be achieved by different experimental means, using simple strain gauges for example. The occurrence of radial cracks at a log end, or lumber crooking, may also evidence growth stresses. We will present methods to evaluate these growth strains. Patterns of growth stress always exhibit very non-linear variations across the diameter: although the stress increment associated to a radius increment has linear variations within the section, the integration of this stress over growth is non-linear. We will present the modelling of some growth scenarios leading to very different growth patterns, and discuss the consequences of the state of prestressing on stem strength: What effect of pre-stressing on tree buckling? What happens in case of wind loading? May a branch break due to its self-loading?
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Dates et versions

hal-01897889 , version 1 (17-10-2018)

Identifiants

  • HAL Id : hal-01897889 , version 1

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Delphine Jullien. Growth stresses and their consequences on tree mechanics. 9th International Plant Biomechanics, Aug 2018, Montréal, Canada. ⟨hal-01897889⟩
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